Traveling with children is stressful enough, but getting turned away at the gate for improper identification can add a new level of inconvenience to the trip. Most airlines make it fairly simple for children to board a plane, but the exact ID requirements for minors vary based on the carrier you’re using, your child’s age and the type of trip you’re taking.

Domestic Flights

According to the Transportation Security Administration's guidelines, a child under age 18 only has to show her boarding pass to board a domestic flight; no additional ID is required. However, each airline has its own policy on identification requirements for children, particularly if you’re paying a reduced rate for a child. For instance, Southwest Airlines offers reduced fares for children between ages 2 and 11, and allows children under age 2 to fly for free as long as they sit on an adult’s lap. To verify a child’s age, Southwest requires you to present a copy of the child’s birth certificate at check-in.

International Flights

Children have the same identification requirements for international travel as adults have. That is, anyone who enters another country must have a passport. Even newborns must have passports to fly internationally. If you’re getting your child’s first passport, you must bring the child to a passport acceptance facility – many post offices, courts and government offices have this title – to apply. It takes about six weeks to receive the passport, although you can pay a rush fee to receive the document within two weeks. Children must renew their passports every five years until they are 16, after which the passports must be renewed every 10 years.

Unaccompanied Minors

Most airlines let children fly without an adult once they reach age 5. However, various age restrictions apply to unaccompanied minors. For instance, children between age 5 and 7 generally are allowed only to fly on direct flights, and airlines may have their own restrictions. For these reasons, it’s always wise to bring a copy of the child’s birth certificate as proof of age. Tuck a copy into the child’s bag and send another copy to the person who will be putting the child on a return flight.

Other Considerations

Whenever you take your child on an international trip or send her on a plane alone, there are a few other things you should consider. For example, according to the U.S. Department of Transportation, if the child travels internationally with only one parent, some countries require a notarized letter of consent from the child’s second parent or legal guardian before allowing that child to leave and fly home. When sending a child on a flight alone, ask the airline for a gate pass, which allows you to go to the departure gate with your child. Bring your own government identification, such as a driver’s license or passport, to get through security.